Mobile operators are known to share radio communications networks in order to share costs of network establishment, maintenance and operations, particularly in the rollout phase. Network sharing is becoming increasingly popular, due to both the high costs on deploying telecom infrastructure and due to more relaxed regulatory policies.
There are different technical approaches for how a Radio Access Network (RAN) in a cellular mobile network can be shared. One approach is for an operator to own a spectrum license and the second operator to utilize the spectrum of the first operator. This is the case of Mobile Virtual Network Operators (MVNOs), or the case of roaming.
Another approach is for each operator to own a spectrum license and for the hardware equipment to be able to separately handle the two frequency carriers, by creating logical partitions. Hence, the operators share a common hardware, but operate in their respective spectrum band independent of each other.
Yet another approach is for each operator to own a spectrum license, but to jointly use the available spectrum as a common pool of resources. Although this approach is currently not allowed by the regulatory policies in many countries, it possibly will be more widely used in the future.
In yet another scenario, the regulators may change the spectrum licensing policies, from today's policy of allocating spectrum licenses for 10-45 years, to a policy of short-term licenses, e.g., days, hours, or minutes. In this scenario, all the operators would access a common pool of resources, and the spectrum fees could be paid based on consumption. From a technical point of view, this scenario is similar or identical to the approach of using a joint pool of resources.
Additional spectrum allocation policies include scenarios where the license is only assigned for some geographical area which could range from a state or county level down to licensed for individual buildings or microwave links.
A trend related to network sharing is for operators to buy access services from a third party. A typical example is the case of tower operators, which own towers and sites, and sell antenna and base station space to operators. In this case the operators buy access to a passive shared infrastructure. However, there are also cases when the service provider owns an active shared infrastructure. In this case, the Mobile Network Operators (MNOs) are buying radio access in a quite similar way the MVNOs have done traditionally.
The operators may require different service levels from the neutral service provider, depending on the Service Level Agreement (SLA) signed between the two. Ideally, the neutral service provider should be able to sign SLAs and to provide the services to each MNO independently on the SLAs and services provided to the other operators. For instance, an MNO may decide how large should the coverage be for a certain service, in a similar way an MNO with a stand-alone network decide the pace of rolling out a network.
It is known that a radio network with more sites, i.e., with small cells and short distances between the sites, typically has better performance that a radio network with sparser sites. Since the infrastructure cost is roughly proportional to the number of installed and operated sites, there is a natural trade-off between the infrastructure cost and the network performance. The trade-off between the performance and the amount of invested money is typical for any radio network. This can be reflected for instance by the pace with which the operators decide to roll-out their networks. An operator may choose to deploy a network faster than his competitors, which means that the initial performance of the RAN will be better than the competitors' but also that the operator will have higher up-front investments and therefore take larger financial risks.
If the owner of a shared network, e.g., a neutral service provider, is to serve two MNOs with different roll-out strategies, then the number of deployed site depends on the toughest requirement set by the two operators. For instance, this means that the network may have better coverage than what one of the two operators would have liked to have and is prepared to pay for.
Consider for instance the case when an MNO would like to have access to 1000 sites during the first year, while the other MNO would like to have access only to 500 sites. If the neutral service provider is to satisfy the requirement from the first MNO, the shared network would result in 1000 sites although the second operator does not require access and is not prepared to pay or share the costs for more than 500 sites.
If the neutral service provider is to satisfy the requirements of the two MNO independently on which SLA has been agreed with the other MNO, then it will deploy 1000 sites and allow the customers of the second operator to access only half of them. The issue of pricing the services, i.e., splitting the investment costs between the two MNO, is outside the scope of the disclosure.
As long as each MNO operates on a different spectrum resource, there is no technical problem with this approach. However, if the two MNOs are sharing a common pool of resources which could be beneficial to improve the usage of spectrum resources, the end-users of the first MNO will experience performance degradation when the users of the second MNO are restricted from accessing half of the sites, as explained in the following.
FIG. 1 illustrates a shared network consisting of three base stations 111, 112, 113, which are serving three cells 121, 122, 123. A first operator buys access only to radio base station 111, while the second operator buys access to all the radio base stations. For instance, this may correspond to the case when the first operator intends to cover only a traffic hotspot, like the center of a city, while the second operator wants to cover a larger area, like the suburbs of that city. The user equipment (UE) 131 belongs to the first operator and it is connected to radio base station 111. Since the UEs of the first operator are not allowed to access radio base stations 122 and 123, the coverage of cell 121 is much larger than the coverage of cells 122 and 123. Moreover, the coverage of cell 121 overlaps with the coverage of cells 122 and 123, although they use the same pool of radio resources. However, the data-rate provided by this large cell 121 is low, exemplified by the height of curve 141. If UE 131 was allowed to connect to the other cells, then the data-rate could have been as indicated by the dashed curve 142. The problem is that, when being connected to BS 111 through the link 151, the UE 131 generates a lot of uplink interference to radio base station 113, indicated by the interfering link 152. Similarly, the radio base station 113 will generate a lot of interference to the link 151 in the downlink direction. Thus, in this scenario both operators will see degraded network performance.
Hence, the price of handling different roll-out policies with the state-of-art techniques is performance degradation, which may be too high to justify the cost savings obtained by sharing the resources.
Similar problems can be seen in scenarios where each operator has its own site placed at geographically different but bordering locations and are using the same spectrum e.g. when the spectrum allocation policy is based on location.